The use of adsorption to purify fluid streams is known. During the process of adsorption, an immobolized molecule (known as a "ligand") forms a chemical bond with another molecule carried by a fluid stream (known as the "ligate"). The ligand thus removes the ligate from the fluid stream, thereby purifying the fluid stream.
It is desirable that the ligand which is used have a highly selective binding constant for the target ligate, so that other substances in the fluid stream whose removal is not desired are not bound by the ligand. Highly selective ligands, however, tend to be costly.
One way of reducing the overall cost of a specific adsorption system is to employ a ligand which is capable of regeneration. A regenerable ligand has a binding constant which, under one set of circumstances, is high and which, under another set of circumstances, is low. During the latter circumstances, the ligand will release any bound ligate and is thereby made available for subsequent use.
Short cycles of adsorption and regeneration tend to minimize the ligand required to achieve a given rate of ligate removal (e.g., in grams per minute), and thus further reduce the overall cost of the adsorption system. Conventionally, the regeneration agent is conveyed to the ligand along the same fluid path which the ligate follows. Therefore, the possibility of shortening the cycle length is ultimately limited by the time required to displace a ligate-bearing fluid stream from the fluid path, replace it with the regeneration agent, then displace the regeneration agent, and finally reintroduce the ligate-bearing fluid stream. Regeneration by conventional methods thus tends to be time consuming and inefficient.
One of the principal objects of this invention is to provide an apparatus and system which purify a fluid stream by adsorption using a ligand which is repeatedly regenerated in a fast and efficient manner.